Aaron T. Pearse
Mississippi State University Department of Wildlife and
Fisheries

Estimates of abundance are critical to manage and conserve
waterfowl and their habitats. Most surveys of wintering waterfowl
do not use probability sampling; therefore, development of more
rigorous methods is needed. In response, we designed and evaluated
an aerial transect survey to estimate abundance of wintering ducks
in western Mississippi during winters 2002-2004.

We designed a probability-based survey using stratified random
and unequal probability sampling of fixed-width transects. To
correct for visibility bias inherent in aerial surveys, we
conducted an experiment to model bias and incorporated correction
factors into estimation procedures to produce adjusted
estimates.

Bias-corrected estimates were most accurate. Precision of
abundance estimates of total ducks met a priori goals (CV ≤ 15%) in
10 of 14 surveys. Based on a simulation study, the implemented
survey design provided the most precise estimates, yet certain
refinements remained possible.

We also illustrated potential applications of survey results in
the context of conservation and management of wintering waterfowl
populations and habitats. We described patterns of abundance within
and among winters, including a comparison with surveys conducted
during winters 1988-1990 that revealed mallard abundance decreased
65% from the late 1980s. We developed a method to illustrate
population abundance spatially for scientific and public education.
We attempted to explain temporal variation in abundance estimates
relative to variables potentially representing hypotheses
explaining regional distributions of ducks. We concluded the data
provided stronger support for factors related to energy
conservation by ducks than factors related to energy acquisition.
Finally, we determined associations between duck distributions and
habitat and landscape features in accordance with the
habitat-complex conceptual model. Landscapes with greater
interspersion and diversity of wetlands attracted increased numbers
of ducks, although other factors such as wetland area also were
important.

We concluded that this study advanced methodologies to survey
wintering waterfowl. Although improvements were warranted, we
recommend this survey design for continued monitoring of wintering
ducks in western Mississippi. Furthermore, we suggest habitat
management on public and private lands should include complexes of
seasonally flooded cropland, moist-soil, forested, and permanent
wetlands to potentially increase wintering duck numbers in western
Mississippi.